This research is a continuation of studies on the amino acid sequences of tubulin and actin from calf brain. One of thirteen cyanogen bromide-produced fragments of the alpha chain of tubulin, the sequences of eight have been determined. The project involves the isolation and sequencing of the remaining five peptides, which make up 80% of the molecular weight of the alpha-chain, and alignment of the cyanogen bromide peptides by isolation of methionine-containing tryptic peptides. Studies on the beta-chain will be focussed upon the peptide which arises from the carboxyl terminus, and the sequence of the rest of the chain will be studied after the sequence of the alpha-chain is completed. Thirteen out of seventeen cyanogen bromide peptides of brain actin have been purified and the sequences have been partially determined. Purification and sequencing of the remaining four peptides as well as completion of the sequences of the peptides that have been isolated will be carried out in parallel. Based on the information about primary structure, we shall study the functional properties of the molecules and correlate them with the role of specific amino acid side chains.